Fifty-nine patients with acute leukemia were studied by flow cytometry using monoclonal antibody against DNA polymerase alpha. Since fresh and frozen cells showed identical flow cytometric histograms, 86 cryopreserved samples (39 from peripheral blood and 47 from bone marrow) were used in this study. The DNA polymerase alpha-positive population ranged from 16.3 to 84.7% in peripheral blood, and from 6.5 to 92.1% in bone marrow. A positive correlation (r = 0.80; p < 0.01) was found between DNA polymerase alpha-positive populations in peripheral blood and bone marrow from the same patient. This suggests that the DNA polymerase alpha-positive population in the bone marrow can be estimated from that in peripheral blood. A negative correlation was observed between the positive population in bone marrow samples and the time to reach a nadir (r = -0.58: p < 0.01), while a positive correlation was found between the tumor cell count in bone marrow and the DNA polymerase alpha-positive population (r = 0.64; p < 0.01) in patients who responded to chemotherapy.